1. Technical Field
The invention relates to replacement joint prostheses of the type comprising two parts designed to be anchored in complementary elements of the skeleton and having surfaces for mutual sliding or rolling movement simulating the movements of a natural joint as exactly as possible.
It is particularly, although not exclusively, suitable for use in the field of hip joint prostheses, which are at the present time those most frequently implanted and are particularly well adapted to implementation of the invention. It is however not limited to this particular case and it is equally applicable to prostheses of the knee (which, like those of the hip, have to support the weight of the patient during walking).
2. Prior Art
For a long time it has been postulated that it is necessary to secure rigidly, by cementing, one at least of the parts of the prosthesis. In the case, for example, of the prosthesis of the hip, most of existing prostheses comprise a solid femoral part designed to be anchored mechanically or by cementing in the medullary channel of the femur and an acetabulum unit in the form of a cup designed to be tightly received in a cavity formed in the pelvic bone. Whether the cup is locked by cementing or by screwing or whether it is left free to slide if the two parts come into mutual abutment due to an excess rotation, the prosthesis cannot follow the deformations of the skeleton under load.
An attempt has recently been made to take into account the deformations of the femur under load by imparting some degree of flexure elasticity to the shaft of the femoral part of a hip joint prosthesis. Such construction only contributes a partial and incomplete solution to the problem.